1. Field of the Invention
The present invention relates to a method and apparatus for providing one or more point-to-multipoint services, such as a multimedia broadcast/multicast service (MBMS), to one or more mobile terminals, or user equipment (UE). More particularly, the present invention relates to a method and apparatus for providing one or more services such that, when one or more mobile terminals move to a new area of a mobile communication system managed by a different network element after joining a service, information is transmitted between network elements in a manner that facilitates the continued reception of the service by the mobile terminals that have moved while conserving network resources and increasing efficiency of the mobile communication system.
2. Discussion of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communication system that has evolved from the global system for mobile communications (GSM) system and is directed to providing enhanced services based on the GSM core network and wideband code-division multiple-access technologies.
A conventional UMTS network 1 structure is illustrated in FIG. 1. One mobile terminal 2, or user equipment (UE), is connected to a core network 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains, and manages a radio access bearer for communications between the UE 2 and core network 4 to meet end-to-end quality-of-service requirements.
The UTRAN 6 consists of at least one radio network subsystem 8, including one radio network controller (RNC) 10 acting as an access point to the core network, and at least one Node B 12 managed by a corresponding RNC. The RNCs 10 are logically classified as controlling RNCs, which allocate and manage common radio resources for a plurality of UEs 2 of a cell, and serving RNCs, which allocate and manage dedicated radio resources for a specific UE of a cell. Each Node B 12 manages at least one cell.
Whenever a specific UE 2 is active in a UMTS network 1, there is one RNC 10 acting as its serving RNC 10 (SRNC). The SRNC 10 is the access point to a core network 4 for data transmission of the UE 2. Any other RNC 10 may act as a drift RNC 10 (DRNC). A connection of one UE 2 to the UTRAN 6 may be achieved by the SRNC 10 alone, for example without a drift RNC, but may additionally require one or more DRNC.
An RNC 10 connected to one or more Node Bs 12 via the lub interface controls the radio resources of the Node Bs and is the controlling RNC. The controlling RNC 10 creates a point-to-multipoint relationship with the corresponding Node Bs 12 and controls traffic load and congestion within the corresponding cells and controls code acceptance and code allocation for new radio links.
At any time, information may be transferred between a UE 2 and the core network 4 via the UTRAN 6. Generally, the transfer of information occurs via one RNC 10, for example the SRNC.
However, since a UE 2 is mobile, there are times when the UE moves to a new area, or cell, of a Node B 12 managed by a different RNC 10. When a UE moves to a cell managed by a different RNC 10, the function of a DRNC is necessary. The UE 2 is connected to the SRNC 10 through the DRNC.
FIG. 2A illustrates a portion of the UMTS network 1 of FIG. 1 when a UE 2 is connected to the core network 4 via an SRNC (R1) 10 alone. FIG. 2B illustrates a portion of the UMTS network 1 of FIG. 1 when a UE 2 is connected to the core network 4 via an SRNC (R1) 10 and a DRNC (R2).
It should be noted that a UE 2 initially completes its connection to the core network 4 via the SRNC (R1) 10 as illustrated in FIG. 2A. However, when the UE 2 moves to a cell managed by the DRNC (R2) 10, the connection between the UE and core network 4 is established through the DRNC (R2) which is connected to the SRNC (R1) via the lur interface. The SRNC (R1) 10 still manages the UE 2 and acts as the access point to the core network 4 while the DRNC (R2) contributes by allocating codes as shared resources and routing user data. The SRNC (R1) 10 and DRNC (R2) are distinguished by the logic related to a specific UE 2 and its specific Node B 12 connection state.
The SRNC (R1) 10 operates with regard to data input via a radio interface or data transmitted to the UE 2 and allocates radio resources appropriate for providing services. Radio resource management functions are control functions related to a specific UE 2 and include transmission channel establishment, handover decisions and open loop power control.
A radio resource control (RRC) layer is defined on a third layer of the radio interface protocol for each RNC 10 and UE 2. The RRC layer is responsible for controlling transport and physical channels in association with establishment, reconfiguration, and release of a radio bearer, which is a service provided by a second layer of radio interface protocol and which is established in order to transfer data between a UE 2 and the core network 4. The establishment of a radio bearer defines the behavior of a protocol layer, for example the channel characteristics needed to provide a specific service, and is a process of setting up an operational method of the service and its parameters.
When an RRC layer of a specific UE 2 and an RRC layer of an RNC 10 are connected for the exchange of RRC messages, the UE is said to be in an RRC-connected mode. In the absence of such a connection, the UE 2 is in the RRC idle mode. The serving RNC (R1) 10 of a UE 2 is determined when an RRC connection to an RNC is established. The RNC 10 recognizes and manages the corresponding UE 2 according to a cell unit.
An RNC 10 is unable to recognize the presence of UEs 2 in the RRC-idle mode. The core network 4 manages UEs 2 in the RRC-idle mode, specifically by the MSC or SGSN, according to location or routing area, which is an area greater than one cell. Although a UE 2 in the RRC-idle mode may receive multimedia broadcast/multicast service (MBMS) data, the UE must be in the RRC-connected mode to receive general mobile communication services, such as voice and packet data.
An MBMS is a service providing streaming or background service to a plurality of UEs 2 via downlink-dedicated MBMS bearer services. In the UTRAN 6, an MBMS bearer utilizes point-to-point (p-t-p) or point-to-multipoint (p-t-m) radio bearer services.
As the name implies, an MBMS may be performed in a broadcast mode or a multicast mode. In the broadcast mode, multimedia data is transmitted to all users within a service area, for example the domain where the broadcast service is available. In the multicast mode, multimedia data is transmitted to a specific user group within a service area, for example the domain where the multicast service is available.
FIG. 3 illustrates the concurrent events of a specific UE 2 and a specific MBMS in a multicast mode transmission. A UE 2 desiring to receive an MBMS completes a subscription procedure in order to establish a relationship between the UE and the provider of the MBMS. All subscribing UEs 2 should receive a start service announcement provided by the core network 4 which corresponds to the specific MBMS and informs subscribing UEs 2 of a list of services to be provided and associated information.
To participate in the specific group of UEs 2 receiving a specific multicast service, a UE “joins” a multicast group by notifying the core network 4 of an intention to receive the specific multicast service. To terminate participation in the group, a UE 2 performs a “leave” operation. Subscription, joining, and leaving are performed by each UE 2 for each service and may be carried out at any time prior to, during, or after the data transfer.
While the specific MBMS is in progress, for example at some time after transmission of a “session start” command but before a “session stop” command is received, one or more sessions of the service may sequentially take place. A session corresponds to a period of data transfer. When an MBMS data source has MBMS data ready for transfer, the core network 4 informs the RNC 10 of a session start. When it is determined that there will be no data transmission available for an extended period of time, for example a long idle period, the core network 4 informs the RNC 10 of a session stop. Data transfer for the specific MBMS can be performed only for the time between the session start and the session stop and only UEs 2 having joined the multicast group for the specific MBMS are enabled to receive the MBMS data.
In the session start process, the RNC 10 transmits an MBMS notification to participating, or joined, UEs 2 after receiving a session start from the core network 4. The MBMS notification is transmitted at least once before MBMS data transmission and informs the UEs 2 that the data transfer of a specific MBMS in a prescribed cell is imminent.
Upon a session start, the RNC 10 recognizes and performs a count of the joined UEs 2 within a specific cell. As a result of the counting process, the RNC 10 determines whether to establish a point-to-point or point-to-multipoint radio bearer according to a set threshold. The RNC 10 establishes a point-to-point MBMS radio bearer if the number of joined UEs 2 is below the threshold and sets up a point-to-multipoint MBMS radio bearer if the number of joined UEs 2 exceeds the threshold.
Once the MBMS radio bearer is determined, the RNC 10 informs the UEs 2 accordingly. If a point-to-point radio bearer is determined, all the joined UEs 2 for a specific service are requested to transition to the RRC-connected mode to receive MBMS data. On the other hand, such a transition is unnecessary if a point-to-multipoint radio bearer is determined since reception via a point-to-multipoint radio bearer is enabled even for UEs 2 in the RRC idle mode. If the counting process determines that there is no UE 2 desiring to receive the service, no radio bearer is established and no MBMS data is transmitted in order to avoid the unnecessary consumption of radio resources.
When the MBMS data for one session of the specific MBMS is received from the core network 4, the RNC 10 transmits the data using the established radio bearer. Upon receiving the session stop, the RNC 10 releases the established radio bearer. A new radio bearer must be established for each subsequent session. If there is no further session scheduled, a stop service announcement is transmitted.
The MBMS transmission process is executed between the UEs 2 and the core network 4, as well as higher layers, for each service via the controlling RNC 10. If a UE 2 remains in a cell managed by the RNC 10 at the time of RRC connection, the MBMS transmission process is executed according to the configuration illustrated in FIG. 2A, for example using only the serving RNC (R1) 10. Should a drift RNC (R2) 10 be necessary, the configuration illustrated in FIG. 2B is applicable and the UE 2 is connected to the higher layers via at least one drift RNC (R2) 10 and the serving RNC (R1).
In the conventional MBMS transmission process, an RNC 10 providing a specific MBMS recognizes and manages a UE 2 in the RRC-connected mode among UEs joining a specific MBMS in each cell. The RNC 10 manages a list of UEs 2 in the RRC-connected mode for each MBMS in each cell in order to identify each UE that has joined the specific MBMS by its radio network temporary identifier (RNTI).
An MBMS attach process is performed for UEs 2 in the RRC-connected mode that move from a cell managed by the serving RNC (R1) 10 to a cell managed by a drift RNC (R2). The attach process is performed when an MBMS that a moving UE 2 has joined is in progress during the move or when a session start command is received from the core network 4 after the UE has moved.
FIG. 4 illustrates a conventional MBMS attach process 50 when an RRC-connected UE 2 moves from a cell of the serving RNC (R1) 10 to a cell of a drift RNC (R2). The serving RNC (R1) 10 transmits an MBMS attach request message to the drift RNC (R2) in step S52. The MBMS attach request message includes information related to the moved UE 2 and the drift RNC (R2) adds an identifier of the moved UE to a list of RRC-connected UEs. The list of RRC-connected UEs 2 includes UE identifiers for each MBMS.
Upon receiving the MBMS attach request message for a specific UE 2, the drift RNC (R2) 10 determines whether a resource for maintaining the RRC-connected mode of the UE can be allocated. If a resource for maintaining the RRC-connected mode of the UE 2 can be allocated, the drift RNC (R2) 10 attaches the identifier of the UE to the list of RRC-connected UEs for the MBMS that the UE has joined and transmits an affirmative response to the serving RNC (R1) via an MBMS attach response message in step S54. On the other hand, if no radio resource is available, the drift RNC (R2) 10 rejects the request and transmits a negative response to the serving RNC (R1) in step S54.
Upon receiving the affirmative response in the MBMS attach response message, the serving RNC (R1) 10 maintains the RRC connection of the UE 2 in the new cell. The serving RNC (R1) 10 provides the drift RNC (R2) with MBMS data received from the core network 4 and the drift RNC (R2) transmits the MBMS data to the UE 2 via a point-to-point radio bearer.
FIG. 5 illustrates a conventional MBMS detach process 60 performed when a UE 2 in the RRC-connected mode moves from a cell managed by a first drift RNC (R2) 10 to a cell managed by another RNC, for example a second drift RNC (not shown). The serving RNC (R1) 10 transmits an MBMS detach request message for the UE 2 to the first drift RNC (R2) in step S62. The MBMS detach request message includes an identifier of the previous cell where the UE 2 was located before moving, for example the cell managed by the first drift RNC (R2) 10, as well as the MBMS ID and the identifier (RNTI) of the moved UE 2.
The first drift RNC (R2) 10 removes the moved UE 2 from a list of UEs in the RRC-connected mode. The first drift RNC (R2) 10 may transmit a response to the serving RNC (R1) via an MBMS detach response message in step S64.
According to the conventional methods illustrated in FIGS. 4 and 5, the serving RNC (R1) 10 transmits one MBMS attach request message or one MBMS detach request message to a drift RNC (R2) for each UE 2 per joined MBMS. More specifically, when the serving RNC (R1) 10 transmits an MBMS attach request message or an MBMS detach request message to the drift RNC (R2), one request message is transmitted for each specific MBMS among a plurality of such services that a specific UE 2 may have joined.
If a UE 2 joins more than one MBMS and if several such services are in progress, the MBMS attach and MBMS detach request messages are transmitted a corresponding number of times, for example once for each service in progress for a given UE. Furthermore, if several UEs 2 join one MBMS and several of the joined UEs move from the cell managed by the serving RNC (R1) 10 to a cell managed by a drift RNC (R2) while the MBMS is not in progress, the serving RNC (R1) transmits MBMS attach messages several times to each joined UE upon receiving a session start command for the MBMS.
When the conventional methods are performed, the frequency of MBMS attach/detach request message transmission increases according to the number of mobile terminals joining an MBMS and according to the number of such services provided. Therefore, the signaling load between the serving RNC and the drift RNCs increases and the efficiency of network resources is reduced accordingly whenever a mobile terminal moves to a cell managed by a new drift RNC. Therefore, there is a need for a method and apparatus that facilitates providing an MBMS to a mobile terminal that moves to a cell managed by a new drift RNC while minimizing the corresponding increase in the signaling load between the serving RNC and drift RNC and maintaining the efficiency of network resources. The present invention addresses these and other needs.